【正确答案】 C

【答案解析】[解析] unless引导条件状语从句，表示“除非……”。通常情况下，条件状语从句主要是由if或unless引导，例如：They have a meeting every Friday, unless there is nothing to discuss．(他们每星期五开一次会，除非没有事情可商谈。)If I were you, I'd go to night school．(我要是你，我会去上夜校。)